Method and apparatus for working metal



`lune 27, 1967 J. w. HlNsHAw 3,327,513

METHOD AND APPARATUS FOR WORKING METAL Filed Feb. l2, 1965 v 2 meets-sheet 1 IN V EN TOR.

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METHOD AND APPARATUS FOR WORKING METAL Filed Feb. l2, 1965 2 sheets-sheet 2 IN V EN TOR.

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United States Patent O 3,327,513 METHQD AND APPARATUS FOR WRKING METAL John W. Hinshaw, 11122 Vinevale, Garden Grove, Calif. 92641 Filed Feb. 12, 1965, Ser. No. 432,286 22 Claims. (Cl. l2-367) The present invention relates to the drawing of metal tubing, and it relates particularly to methods and apparatus for drawing tubing which is initially of uniform diameter so as to apply a taper to the tubing.

Various methods have heretofore been employed for tapering metal tubing, but the prior art methods have generally proven to be slow and expensive, seriously limited as to the amount of taper which can be applied to the tubing, restricted as to the tubing compositions which can be handled and as to the wall thickness which can be accommodated, and in many instances introduced undesirable variations in the tubing wall thickness. Many shapes of tapered tubing have heretofore not been produceable by prior methods, or if they could be made, required a large number of successive operational steps. Uniformity of production control has also been a serious problem in connection with prior art tube tapering methods, the shape of the taper and the wall thickness often varying from part to part during production, which is a serious disadvantage in many instances where identity of shape and wall thickness is important for an entire run of iinished parts.

In View of these and other problems in the art, it is an object of the present invention to provide a novel method and apparatus for applying a taper to tubing which is initially of uniform diameter, wherein a drawing ring of novel shape and composition is employed to draw the tubing against a tapered mandrel without altering the wall thickness of the tubing, whereby to produce a tapered tube of accurate predetermined dimensions, both as to the taper and as to the wall thickness.

Another object of the present invention is to provide a method and apparatus for tapering tubing which requires only a single drawing operation and utilizes only a single drawing ring, regardless of the amount of taper which is to be put into the tubing, regardless of the diametrical size of the tubing which is being tapered, regardless of the wall thickness of the tubing, and regardless of the composition of the metal in the tubing.

Another object of the present invention is to provide a novel method of applying a taper to tubing by combining both drawing and spinning in a single operation, thus permitting extremely thick or tough tubing to be formed to a taper.

Another object is to provide a method of drawing tapered tubing wherein a plurality of laminated tubes are drawn together so as to provide a tapered finished product which has a plurality of laminations that are tightly and uniformly bonded together in a permanent state of compression relative to each other.

A further object of the invention is to provide a method of tapering tubing which produces stepped variations in the diameter of the tubing, rather than a continuous taper, yet which employs only a single drawing operation.

Another object is to provide a method of drawing tubing wherein a controlled taper or other variation in the Wall thickness of the tubing is combined with a controlied overall taper in the diameter of the tubing.

A further object is to provide a novel method of tapering tubing wherein the tubing is tapered downwardly from a relatively large diameter to a relatively small diameter, and then back outwardly to a relatively large diameter, as for the production of a venturi tube, yet which requires only a single drawing operation.

Additional objects and advantages of the invention will appear during the following part of this specification wherein the details of construction, mode of operation and novel method steps of a preferred embodiment are described with reference to the accompanying drawings, in which:

FIG. l is a side elevation View of a mandrel employed in the present method.

FIG. 2 is a side elevation view of a tube to be drawn, the tube being necked down at one end for securing the tube against axial sliding relative to the mandrel during the drawing operation.

FIG. 3 is an axial section, partly in eievation, illustrating the tubing of FIG. 2 mounted on the mandrel of FIG. l, with the drawing ring and supporting and actuating structure in position for the commencement of a drawing operation.

FIG. 4 is a view similar to FIG. 3, with the drawing operation approximately one-half completed.

FIG. 5 is a view similar to FIG. 4, with the drawing operation substantially completed.

FIG. 6 is an axial section showing a presently preferred `drawing ring.

FIG. 7 is an axial section similar to FIG. 6, but illustrating a variation of the drawing ring particularly adapted for accommodating large tapers.

FIG. 8 is a view similar to FIG. 4, illustrating the drawing of laminated tubing.

FIG. 9 is a cross-sectional view illustrating the use of a mandrel of non-circular cross-section which may be employed in the present invention.

FIG. l0 is a fragmentary side elevation view illustrating a tapered `mandrel which is stepped in construction for providing stepped tapered tubing.

FIG. 1l is an axial section, partly in elevation, illustrating a method and apparatus for first tapering the tubing down to a reduced diameter and then tapering the tubing back out to an enlarged diameter, as for producing a venturi tube.

FIG. 12 is a view similar to FIG. 11, but with the drawing operation approximately one-half completed.

FIG. 13 is a view similar to FIG. 12, but with the drawing operation approximately three-quarters completed.

Referring to the drawings, FIG. l illustrates a mandrel l0 for use in the present invention,the mandrel having an accurately finished tapered working surface 12, and having axially projecting end shafts 14 and 16 which are engageable by suitable supporting structure for moving the mandrel axially during operation, either by pushing from the large end of the mandrel or by pulling from the small end of the mandrel. Flats 18 may be provided in the end shaft 16 for gripping the mandrel so that it can be pulled to the right in FIG. l.

FIG. 2 illustrates a section of tubing 20 which has been necked or nosed radially inwardly at 22 as by swedging or spinning to a reduced diameter for engagement against the small end of the mandrel so as to secure that end of the tubing to the mandrel to prevent axial slippage of the tubing relative to the mandrel during the drawing operation.

A pair of actuating plate members 24 and 26 are disposed generally at opposite ends of the mandrel 10 at the beginning of the drawing operation, and these plates 24 and 26 are actuated so as to move toward each other during the drawing operation to move the mandrel and the tubing which is supported thereon relative to the drawing ring employed in the invention. This relative motion between the plates 24 and 26 may be accomplished by having either plate stationary, while the other plate is moved toward the stationary plate. The end shaft 14 of mandrel 10 is supported in a positioning recess 2S in the end plate 3 24, while the other end shaft 16 extends through an opening 29 in end plate 26.

The end plate 26 is provided With a recessed face 30 against which a holder 32 abuts, the holder 32 providing support means for the drawing ring 34 employed in the present invention. This holder 32 is preferably provided in the form of a segmented ring comprising a pair of semicircular segments 36 and 38 which are resiliently biased toward each other by means of a spring loop 40 disposed thereabout. The holder 32 is provided with axial aperture 42 through which the mandrel 10 and tubing 20 pass during the drawing operation, and the holder 32 is axially recessed at 44 for receiving the rear end portion of the drawing ring 34, the contracting force of spring loop 4t) on the segments of holder 32 causing the drawing ring 34 to be resiliently gripped between the segments 36 and 38 of holder 32, which function in much the same manner as a vise.

The details of construction of the presently preferred form of drawing ring 34 employed in the invention are best shown in FIG. 6 of the drawing. The ring 34 has front and rear ends 46 and 48, respectively, has an outer periphery 50 which is of generally cylindrical form, and has an inside surface S2 which commences at the rear end 48 in a short land portion 54, which is the most constricted part of the inside surface 52, the surface 52 curving forwardly and outwardly so as to meet the outer periphery 50 at the front end 46 of the ring.

The inside diameter of the land portion 54 `of the ring is preferably slightly less than the diameter of the mandrel at its small end plus twice the wall thickness of the tubing to be drawn, so ythat the land region 54 of the ring will tightly compress the tubing against the narrow end of the mandrel at the commencement of the drawing operation. The forwardly facing, outwardly flaring contour of the inside surface 52 of drawing ring 34 is required so that the drawing ring will not cut into the bulge of the tubing which is immediately in front of the drawing ring in the early stages of the drawing operation. In order for the flare in the ring to be most effective in preventing damage to the tubing, it is preferable to provide a ring 34 which has an outer diameter approximately as large as the diameter of the tubing which is to be drawn, although satisfactory results have been obtained with ring diameters which are somewhat smaller than the outer tubing diameter. Aedquate curvature of the forwardly flaring inside surface 52, and adequate material in the ring to accomplish the drawing operation, are best provided by having the wall thickness of the ring from the land 54 to the outer periphery 50 approximately equal to the radial distance from the surface of the mandrel at the small end of the mandrel to the outer diameter of the tube which is being drawn.

The length of the drawing ring 34 between the front and rear ends 46 and 48, respectively, will be varied according to the toughness of the material of the tubing. Thus, where a relatively malleable and formable material is embodied in the tubing, such as copper, a relatively short ring 34 may be employed. However, where arelatively tough material, such as steel, is used in the tubing, a considerably longer ring 34 is employed so as to provide the necessary tensile strength in the ring.

Where a relatively large amount of taper is being applied to the tubing so that the thickness of the ring would be such as to provide too much material in the ring in order to give the desired amount of outward flaring of the inside surface of the ring, it may be desirable to provide a ring such as the ring 34a shown in FIG. 7 wherein a portion of the ring material is removed from the outer peripheral region adjacent to the rear end 48a of the ring. This reduction of the outer diameter of the ring proximate the rear end 48a is designated by the numeral 56 in FIG. 7, and any desired amount of the material may be removed from this region without altering the contours of the operative surfaces of the ring. The particular ring illustrated in FIG. 7 has a radial distance between the land portion 54a and the outer peripheral portion 50a which is approximately as great as the radial distance from the axial center to the land portion 54a, and is designed to provide a large amount of taper in the tubing; for example, an amount such that the small end of the taper would be only about one-half of the diameter of the large end of the taper. The amount of metal which would have been in the ring 34a if the outer region had not been reduced as at 56 would have been so much that there would be alikelihood of ironing or thinning out the tubing during the drawing operation. On the other hand, it is the purpose of the present invention to draw tubing without any substantial thinning of the wall thickness of the tubing which is being drawn.

The drawing ring must have sufcient tensile strength so as to be able to flatten the tubing wall down tightly and solidly against the surface of the mandrel, while at the same time the ring must be formable and not brittle, so as to continuously form to the changing shape of the mandrel as the ring passes axially over the mandrel and the tubing. I have found from extensive experiments that one material has particular suitability for use in the drawing ring 34, in order to accommodate the widest possible variation in the amount of taper which can be applied to a tube, the size of the tube, the wall thickness of the tube, and the composition of the tube. This preferred material is brass which comprises between and 90% copper, and which preferably has about copper content. Pure copper has been found in practice to be too weak, tending to split and leave a ridge in the tubing workpiece. Actually, it has been found from practice that brass compositions having more than copper content are too soft for general use. On the other hand, it has been found that brass compositions of less than 80% copper are too brittle for most uses, breaking when a substantial taper is being applied to the tubing. This breaking will occur regardless of the initial condition of temper of the brass, as the process of the present invention causes the drawing ring to be work-hardened.

For the same reason, the condition of temper of the drawing ring 34 employed in the invention where the ring is made of the preferred material does not substantially affect the process, as the preferred material will work-harden so as to have the necessary strength characteristics.

Employing drawing rings 34 of the preferred composition as aforesaid, extensive tests have shown that the present method is suitable for accurately drawing tubing without leaving any ridges therein, and without altering the wall thickness of the tubing, where the tubing is composed of brass, copper, nickel, aluminum, stainless steel, and b-oth welded steel tubing and cold-drawn seamless steel tubing. Accordingly, the present invention appears to be suitable for use in connection with practically any type of metal tubing.

Although the method of the present invention will normally not alter the wall thickness of the tubing, a variation of the present invention can be employed so as to provide a tapered or otherwise varying wall thickness in combination with tubing which is tapered in its overall size. This maybe accomplished by disposing the tubing over a mandrel which varies slightly from a perfectly cylindrical form, for example, a slightly tapered mandrel, and then drawing the mandrel and tube through a sizing die of fixed internal dimensions. This will -alter the wall thickness of the tubing according to the shape of the mandrel, for example, applying a taper to the wall thickness. This tubing having varying wall thickness is then treated in exactly the same manner as hereinabove described in connection with FIGS. 1-7, being laid out tightly on the working surface 12 of the mandrel 10. Because of the fact that my drawing ring 34 accommodates itself to the thickness of the mandrel plus the thickness of the tubing, regardless of what the tubing thickness might be, the drawing ring 34 will not `further lalter the tubing thickness, whereby the nal product will be a combination of the varying tubing wall thickness, such as a tapered Wall, and an overall taper in the tubing.

A further variation in the present process which is useful in the drawing of particularly thick or tough tubing, is to provide relative rotation between the drawing ring and the mandrel, whereby to combine the drawing operation with a novel spinning operation wherein the gripping is confined around its entire periphery. This combined drawing and spinning operation, like the drawing operation alone, does not alter the wall thickness of the tubing.

Referring now to FIG. 8 of the drawings, I have there illustrated the simultaneous drawing of a pair of telescoped tubes, an inner tube 518 and an outer tube 60. The tubes 58 and 60 may be of the same materi-al, or may comprise two different materials, such as steel and aluminum or any other two metals. The two tubes are disposed in telescoping relationship and are necked down over the small end of the mandrel as heretofore described, and they are then drawn in the same manneras a single tube. The drawing operation lays the two tubes solidly down against the mandrel, and bonds the tubes together in a permanent state of compression.

In FIG. 9 I have illustrated a cross-sectional view of a mandrel having a non-circular cross-section, the particular mandrel 62 illustrated in FIG. 9 being hexagonal. I have found in practice that the present drawing method is suitable for drawing circular tubing to such irregular cross-sectional shapes. Any of a wide variety of crosssectional shapes may be imparted to the tubing by applying a die having a complementary cross-sectional shape, and the cross-sectional shape may vary along the length of the mandrel. For example, the shape may commence as a circular section and may then vary to a square or other polygon, or vice versa, or it may vary from one non-circular shape to another, as desired, so long as there are no grooves in the mandrel.

In FIG. 10 I have illustrated a mandrel 64 of stepped, tapered construction, which I have also found to be suit- -able for use in connection with the present invention. My drawing ring 34 will lay the tubing solidly against a mandrel such as that shown in FIG. 10, the tubing conforming not only to the elongated tapered portions, but also to the intermediate step portions, and the wall thickness of the tubing is not altered by the process. A mandrel of the type suggested in FIG. l0 permits such products as `golf club shafts to be produced by the present invention without varying the wall thickness of the tubing and by employing only the single drawing step of the present invention, as compared with previous processes which required many steps and resulted in an altered wall thickness of the product.

Referring now to FIG. 11, I have there illustrated an embodiment of the invention which permits tubing to be drawn down `from a relatively large diameter to a relatively small diameter, and then drawn back up to a larger diameter, thus permitting the drawing of a tube which will are outwardly toward both of its ends from a reduced central portion, as for a venturi tube.

This process is accomplished by employing a separable mandrel 66 having a pair of tapered mandrel portions 68 and 70 which are adapted to be axially aligned and in abutting relationship at their narrow ends. Suitable aligning means may be provided for interlocking the small ends of the mandrel portions 68 and 70 so as to retain them in alignment.

A back-up plate 72 is provided, and has an axial opening 74. The separable mandrel 66, and a tube supported thereon and necked over the large end of the mandrel portion 68, are adapted to move axially through the opening 74- in back-up plate 72. The back-up plate 72 has a forwardly facing recess 76 which serves as a seat Ifor holding the rear end 78 of drawing ring 8i). The drawing ring employed in this embodiment of the invention preferably has cylindrical, generally parallel outer and inner walls, the outer wall being bevelled inwardly at the front end 82 of the rin-g, and the inner wall being bevelled outwardly fat the front end of the ring.

A split die 84 is supported relative to the back-up plate 72 so as to be movable toward the back-up plate 72, as by hydraulic actuating means (not shown), and it is preferred to move the die 84 toward the .back-up plate 72 at a rate which is correlated to the movement of the tapered mandrel portion 68 through the back-up plate 72. The die 84 comprises die halves 86 and 88 which are held together until the tapered mandrel portion 68 has moved through the ring, and then which are separated and moved out of the way as best shown in FIG. 13. Die 84 has a tapered inside cam face which cams the front end 82 of ring 80 radially inwardly as the die 84 moves toward the back-up plate 72 and as the mandrel portion 68 is moving through the back-up plate 72, whereby the tube 20 will be drawn down against the tapered mandrel 66 as the forward portion of the ring is continuously cammed inwardly. It will be apparent that the bevelled outer edge at the front end 82 of the ring cooperates with the die cam face 90 so as to provide excellent control of the inward camming of the ring. The bevelled inner edge at the front end 82 of the ring 80 prevents the ring from cutting into the tubing, particularly as the die moves over the narrow center portion of the separable mandrel 66.

When the tube 20 has been been drawn down to the junction between the mandrel portions 68 and 70, the die halves 86 and 88 are separated and the ring 80 then performs in the same manner as the ring 34 shown in FIG. 6.

After the tube 2d has been completely drawn against the mandrel 66, the necked down portion of the tube at the large end of the mandrel portion 68 is cut away, and the mandrel portions 68 and 70 may then be withdrawn from the opposite outwardly flaring ends of the finished tube. In a situation where the taper fiares outwardly only in one direction, as with the steps shown in FIGS. 1-10, the tube is merely withdrawn off of the small end of the mandrel.

I have also discovered that tubing can be tapered down from a relatively large diameter to a relatively small diameter by squeezing a drawing ring radially inwardly in much the same manner as described above in connection with FIGS. 11, 12 and 13, but by merely gripping the large end of the tubing without employing a downwardly or radially inwardly tapering mandrel section like the mandrel portion 68. This provides greatly increased flexibility of the present process, permitting a section of the tubing to be tapered inwardly without a mandrel, then a next section of the tubing to be tapered outwardly over a tapered mandrel starting at the small end thereof with the drawing ring unconfined about its periphery, and then tapered back inwardly by removing the tapered mandrel and again axially squeezing the ring so as to cam the ring radially inwardly within a die like die 84. This sequence of operation may be repeated any number of times with the same ring, starting with either an inwardly tapering step or an outwardly tapering step.

While the instant invention has been shown and described herein in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed herein, but is to be accorded the full scope of the claims.

What I claim is:

1. The method of drawing tapered tubing which comprises the steps of: placing a length of tubing over an elongated mandrel which has a working surface that tapers from a relatively small end to a relatively large end; holding the tubing against longitudinal movement over the mandrel in a direction from the small end toward the large end of the mandrel by necking the tubing down over the small end of the mandrel so that the inside of the tubing adjacent to the small end `of the mandrel is smaller than the working surface of the mandrel at that end; and moving the mandrel and tubing axially through an annu- -lar metal drawing ring starting with the small end of the mandrel and working toward the large end so as to draw the tubing tightly against the working surface of the mandrel without substantially altering the wall thickness of the tubing, said drawing ring being of one-piece construction and of uniform composition throughout with its outer peripheral surface generally unconned, and having a uniform cross-sectional shape about its entire circumference; and concentrating the radially inwardly directed drawing force of the ring against the tubing generally rearwardly in the ring by having the ring relatively thin proximate the leading end of the ring and relatively thick proximate the trailing end of the ring.

2. The method of claim 1 wherein the ring is composed of brass having a copper content ranging from about 80% to about 90%.

3. The method of claim 1 wherein the ring is composed of brass having a copper content of about 85%.

4. The method of claim 1 wherein the drawing ring and mandrel are continuously rotated relative to each other during the drawing operation so as to combine the drawing with a circumferentially confined spinning of the tubing, without substantially altering the wall thickness of the tubing.

5. The method of claim 1 wherein at least a portion of the mandrel is non-circular in cross-section so as to provide a drawn tube having at least a portion thereof non-circular in cross-section.

6. The method of claim 1 wherein the tubing is caused to flow continuously from its unconstricted form ahead of the ring to its drawn form within the ring by having the inside surface of the ring flare forwardly and radially youtwardly to the leading end of the ring in a continuous curve from an innermost land portion of the ring proximate the trailing end of the ring.

7. The method of claim 6 wherein the radial thickness of the ring between the inside of the land portion of the ring and the outside surface of the ring proximate the leading end of the ring at the beginning of the drawing is approximately equal 4to the amount of taper in that portion of the Working surface of the mandrel against which the tubing is drawn.

8. The method of claim 6 wherein the outside surface of the ring between the leading and trailing ends =of the ring is cylindrical.

9. The method of claim 7 wherein the outer peripheral region of the ring is notched `out proximate the trailing end of the ring so that the radial distance from the inside of the land portion of the ring and the outside surface of the ring proximate the trailing end of the ring is less than the radial distance from the inside of the land portion of the ring to the outside surface of the ring proximate the leading end of the ring.

1t?. The method of producing tapered tubing having a varying wall thickness along the length thereof which comprises the steps of: placing a length of tubing over vla first elongated mandrel which has a working surface that varies in radius an amount less than the wall thickness of the tubing; holding the tubing and said first mandrel against relative longitudinal slippage; passing said first mandrel and tubing through a sizing die having an orifice of fixed dimensions so as to produce variations in the wall thickness of the tubing; removing the tubing from said first mandrel; placing the tubing over a second elongated mandrel which has a working surface that tapers from a relatively small end to a relatively large end; holding the tubing against longitudinal movement over the second mandrel in a direction from the small end toward the large end of the second mandrel by necking the tubing down over the small end of the second mandrel so that the inside of the tubing adjacent to the small end of the second mand-rel is smaller than the Working surface of the second mandrel at that end; and moving the second mandrel and tubing axially through an annular metal drawing ring starting with the small end of the second mandrel and workin-g toward the large end so as to draw the tubing tightly against the working surface of the second mandrel without substantially altering the wall thickness of the tubing.

11. The method of claim 10 wherein said first mandrel has a tapered working surface so as to apply a taper to the wall thickness of the tubing.

12. The method of drawing tapered tubing which comprises the steps of: placing a length of tubing over an elongated mandrel having relatively small and large ends and having a working surface of stepped, tapered forni comprising a plurality of successive tapered portions and -intermediate curved ramp portions leading from one tapered portion to the next, each individual tapered portion increasing in size toward the large end of the mandrel, and the successive tapered portions inc-reasing in size from the small end to the large end of the mandrel; holding the tubing against longitudinal movement over the mandrel ina direction from the small end toward the large end of the mandrel by -necking the tubing down over the small end of the mandrel so that the inside of the tubing adjacent to the small end of the mandrel is smaller than the working surface of the mandrel at that end; and moving the mandrel and tubing axially through .an annular rnetal drawing ring starting with the small end of the mandrel and working towa-rd the large end so as to draw the tubing tightly against the working surface of the mandrel without substantially altering the wall thickness of the tubing, said ring being of one-piece construction and of uniform composition throughout with its outer peripheral surface generally unconned; and concentrating the radially inwardly directed drawing force of the ring against the tubing generally rearwardly in the ring by having the ring relatively thin proximate the leading end of the ring and relatively thick proximate the trailing end of the ring, whereby said ring will follow the tapered and intermediate ramp portions of the working surface of the mandrel so as to produce a tube of stepped, tapered form.

13. The method of drawing tapered tubing which comprises the steps of: placing a length of tubing over an elongated mandrel which has a working surface that tapers outwardly -to first and second relatively large ends from a smallest point intermediate the ends, the mandrel being axially separable at said smallest point; holding the tubing against longitudinal movement relative to the mandrel at said rst end; holding an annular metal drawing ring about the tubing at said first end of the mandrel between an abutment member and a split die member, said abutment and die members being -apertured so that the mandrel and tubing may pass therethrough, the abutment member engaging the ring proximate its trailing end facing toward said first end of the mandrel and the die having an annular inclined cam surface in its said aperture; simultaneously moving said abutment and die members toward each other so as to cam the leading end of the ring radially inwardly so that the ring will press the tubing tightly against the mandrel and moving the mandrel and tubing axially through said ring so as to draw the tubing tightly against the mandrel -until the ring lies proximate said smallest point of the mandrel; removing the split die from engagement with the ring; moving the remainder of the mandrel and tubing through said abutmentmernber so as to draw the remainder of the tubing tightly against the mandrel; and separating the mandrel at its said smallest point and withdrawing the two mandrel sections from the ends of the tubing, thereby to produce `a tube which tapers outwardly toward its ends from a most constricted portion between its ends.

14. Apparatus for drawing tapered tubing which comprises: a mandrel about which a section of tubing is to be disposed, said mandrel having a working surface which tapers from a relatively small end to a relatively large end; an annular metal drawing ring of uniform composition throughout and having the same cross-sectional shape about its entire circumference; and means engageable with said mandrel and said drawing ring for holding said drawing ring and driving said mandrel and tubing thereon through said ring so as to draw the tubing tightly `against the working surface of the mandrel thereby to taper the tubing without substantially altering the wall thickness of the tubing; said drawing ring being relatively thin proximate its leading end which faces toward the large end of the mandrel and relatively thick at its trailing end so as to concentrate the radially inwardly directed drawing force of the ring against the tubing generally rearwardly in the ring.

15. The apparatus of claim 14 wherein the ring is composed of brass having a copper content lrangi-ng from about 80% to about 90%.

16. The apparatus of claim 14 wherein the ring is composed of brass having a copper content of about 85%.

17. Apparatus for drawing tapered `tubing which comprises: a mandrel about which a section of tubing is to be disposed, said mandrel having a working surface which tapers from a relatively small end to a relatively large end; an annular metal drawing ring of uniform composition throughout having the same cross-sectional shape `about its entire circumference; and means engageable with said mandrel and said d-rawing ring for holding said drawing ring and driving said mandrel and tubing thereon through said ring so as to draw the tubing tightly against the working surface of the mandrel thereby to taper the tubing without substantially altering the wall thickness of the tubing; said drawing ring being relatively thin proximate its leading end which faces toward the large end of the mandrel and relatively thick at its trailing end so as to concentrate the radially inwardly directed drawing force of the ring against the tubing substantially to the rear of the leading end of the ring, and the ring having an inside surface which ares forwardly and radially outwardly to the leading end of the ring in a continuous curve from an innermost land portion of the ring proximate the trailing end of the ring, whereby the tubing is caused to flow continuously from its nnconstricted form ahead of the ring to its drawn form within the ring.

18. The apparatus of claim 17 wherein the radial thickness of the rin-g between the inside of the land portion of the lring and the outside surface of the ring proximate the leading end of the ring is approximately equal to the amount of taper in that portion of the working surface of the mandrel against which the tubing is drawn.

19. The apparatus of claim 17 wherein the outside sur- 10 face of the ring between the leading and trailing ends of the ring is cylindrical.

20. The apparatus of claim 18 wherein the outer peripheral region of the ring is notched out proximate the trailing end of the ring so that the radial distance from the inside of the land portion of the ring proximate the trailing end of the ring is less than the radial distance from the inside of the land portion of the ring to the outside surface of the ring proximate the leading end of the ring.

21. The method of drawing tapered tubing which comprises the steps of: holding an annular metal drawing ring about a length of tubing between an abutment member and a split die member, said abutment and die members being apertured so that the tubing may pass therethrough, the die having an annular inclined cam surface in its said aperture opening toward said abutment member; simultaneously moving said abutment and die members toward each other so that the die will cam the ring radially inwardly against the tubing and moving the tubing axially through said rin-g so as to taper the tubing radially inwardly to a smallest point; removing the split die from engagement with the ring; and moving the tubing and a tapered mandrel within the tubing further in the same direction through the ring so as to draw the tubing upwardly along the mandrel and thereby taper the tubing radially outwardly from said smallest point.

22. The method of drawing tapered tubing which comprises the steps of: moving a section of tubing and a tapered mandrel within the tubing through a drawing ring so as to draw the tubing upwardly along the mandrel and thereby taper the tubing radially outwardly from a relatively small diameter to a relatively large diameter; removing said mandrel from the tubing; engaging the ring between an abutment member and a split die member, said abutment and die members being apertured so that the tubing may pass therethrough, the die having an annular inclined cam surface in its said aperture opening toward said abutment member; and simultaneously rnoving said abutment and die members toward each other so that the die will cam the ring radially inwardly against the tubing and moving the tubing axially through said ring so as to taper the tubing radially inwardly.

References Cited UNITED STATES PATENTS 252,423 1/1882 Buckingham 205-7 414,090 10/1889 Taylor 72-468 431,041 7/ 1890 Fitzpatrick et al 72-96 2,029,552 2/ 1936 Barnhart 205-7 WILLIAM W. DYER, IR., Primary Examiner. G. A. DOST, Assistant Examiner. 

1. THE METHOD OF DRAWING TAPERED TUBING WHICH COMPRISES THE STEPS OF: PLACING A LENGTH OF TUBING OVER AN ELONGATED MANDREL WHICH HAS A WORKING SURFACE THAT TAPERS FROM A RELATIVELY SMALL END TO A RELATIVELY LARGE END; HOLDING THE TUBING AGAINST LONGITUDINAL MOVEMENT OVER THE MANDREL IN A DIRECTION FROM THE SMALL END TOWARD THE LARGE END OF THE MANDREL BY NECKING THE TUBING DOWN OVER THE SMALL END OF THE MANDREL SO THAT THE INSIDE OF THE TUBING ADJACENT TO THE SMALL END OF THE MANDREL IS SMALLER THAN THE WORKING SURFACE OF THE MANDREL AT THAT END; AND MOVING THE MANDREL AND TUBING AXIALLY THROUGH AN ANNULAR METAL DRAWING RING STARTING WITH THE SMALL END OF THE MANDREL AND WORKING TOWARD THE LARGE END SO AS TO DRAW THE TUBING TIGHTLY AGAINST THE WORKING SURFACE OF THE MANDREL WITHOUT SUBSANTIALLY ALTERING THE WALL THICKNESS OF THE TUBING, SAID DRAWING RING BEING OF ONE-PIECE CONSTRUCTION AND OF UNIFORM COMPOSITION THROUGHOUT WITH ITS OUTER PERIPHERAL SURFACE GENERALLY UNCONFINED, AND HAVING A UNIFORM CROSS-SECTIONAL SHAPE ABOUT ITS ENTIRE CIRCUMFERENCE; AND CONCENTRATING THE RADIALLY INWARDLY DIRECTED DRAWING FORCE OF THE RING AGAINST THE TUBING GENERALLY REARWARDLY IN THE RING BY HAVING THE RING RELATIVELY THIN PROXIMATE THE LEADING END OF THE RING AND RELATIVELY THICK PROXIMATE THE TRAILING END OF THE RING. 